VTEC is basically the camshaft switching over to different lobes to give it more power. So from 800(Idle)-4499/4999 it is not in VTEC, and from 4500-5000(I believe those are the actual engagement RPMS, depends on engine) to Redline they are in VTEC.

So...

800-4499/4999 = Not in VTEC
4500/5000-Redline = VTEC